A varistor is broadly used as an over-voltage protection component and surge absorption component of circuit, equipment and components because of its non-linear volt-ampere character. Irrespective whether the varistor is used in power circuitry or electrical circuitry, if transient over-voltage happens frequently, the varistor will operate to suppress over-voltage frequently. At the same time, it will adsorb and release surge energy to protect electrical equipment and components, which will certainly cause the varistor to fail or be damaged. When the varistor suffers transient over-voltage, it will be rapidly partially destroyed and causing fire. Nowadays, most varistors with thermal failure protection have some disadvantages such as the following: Some have a complex structure and slow response rate such as a thermally protected metal oxide varistor which is a traditional module with thermal cutoff device of spring mode such as disclosed in Chinese patent number CNO2222055.0, published on Feb. 12, 2003. Another type is a thermally protected device with a slow response rate or a weak capacity to withstand the capacity of a high surge current such as a traditional safe varistor connected exteriorly with a pellet-type or alloy-type thermal fuse such as disclosed in Chinese patent number CN00237913.9, published on Oct. 31, 2001.